A Text-book of Paper-making

by C. F. Cross; E. J. Bevan

This machine is also adapted so as to carry the cleaned grass to the boiler-house. It is taken forward by means of travelling rakes over the tops of a series of boilers, any one of which can be furnished by simply opening a door corresponding in position with the lid of the boiler.

Boiling.—The ordinary form of boiler is shown in Fig. 24. It is known as a vomiting boiler. The grass is put in by the door E, which is hinged, and is counterbalanced by the weights L. It is securely fastened down by the screws F. Steam enters by the inner pipe A, which dips a little below the perforated false bottom B. Surrounding the steam-pipe is a wider pipe C, open at the top, which is made slightly trumpet-shaped; also open at the bottom, where it ends in a kind of shoulder, on which the false bottom rests. The lower part has two or more openings G cut away, through which the liquor can freely pass.

In order to get as large a charge into the boiler as possible, steam is turned on while furnishing, and a quantity of caustic soda lye is also run in, which has the effect of softening the grass and making it more compact. This is continued until the boiler is well filled.

The action of the boiler is as follows:—The steam passing through the pipe A heats the liquor that has drained from the grass through the perforations in the false bottom, and forcing it up the wide pipe C, causes it to strike against the dome or bonnet D, and distribute itself again over the grass. {92} This is technically known as “vomiting.” In this way a constant circulation of liquor is kept up.

FIG. 24.

The boiler is emptied by the door H and the liquor is run off by the cock I. The boilers are usually supplied with a safety valve E, and also with a pipe for letting off the steam when the boiling is finished. The boiling generally takes from four to six hours. The quantity of soda necessary depends upon the nature of the grass, Spanish requiring less than African. {93}

Routledge, to whom the introduction of esparto as a paper-making material is due, gives 10 per cent. as the proper quantity.

The pressures employed vary from 5 lb. to 45 lb. There has been a growing tendency of late to employ the higher pressures for reasons already stated.